Amplifiers such as operational amplifiers may be used in many electronic circuits to condition, manipulate and amplify signals. In general, an operational amplifier may be designed so that an output signal is proportional to the difference between two input signals. The operating characteristics of an operational amplifier are typically dependent upon its circuit topology. For example, an operational amplifier may include a number of stages such as an output stage that conditions output signals based on the characteristics the output stage and other stages.
While output stage designs may implement various components, field-effect transistors (FETs) such as metal-oxide semiconductor field-effect transistors (MOSFETs) are often incorporated into designs due to their robustness and relatively large operating ranges. To provide amplifiers with low output impedance, FETs may be incorporated into output stage designs in source-follower amplifier configurations. However, compared to bipolar junction transistors (BJTs), the threshold voltage of FETs may vary by significant amounts. These threshold variations may even be present across FETs that are within the same family of devices. In addition to large threshold voltage variations, FETs characteristically have large variations in their temperature coefficients. In general, the temperature coefficient of a FET quantifies the average output voltage change of the FET as a function of ambient temperature. By accounting for variations in temperature coefficient, the performance of an output stage of an amplifier may be improved along with reducing design complexity and production cost.